This invention relates to a photoinitiator and a photopolymerizable composition using said photoinitiator.
Photopolymerizable compositions are extensively used in letterpress printing, formation of relief image, preparation of photoresist, etc. and in these uses of photopolymerizable compositions UV light source is generally used. In these fields, a system of higher sensitivity is more desirable. Particularly when a photopolymerizable composition is put to scanning exposure using laser beam, the composition is required to have a sufficiently high sensitivity to the visible rays (458 nm, 4898 nm, 514.5 nm, etc.) of argon ion laser which is the most powerful light source. In this field, photoinitiator system has repeatedly been studies so far with the aim of enhancing its sensitivity. Although a number of photoinitiator substances such as benzoin and its derivatives, substituted and unsubstituted polynuclear quinones and the like have been disclosed up to today, none of them is known to have a sufficient sensitivity to visible rays.